THE POLYTECHNIC CIVIL ENGINEERING DEPARTMENT

GEOTECHNICAL TECHNICAL REPORT FOR THE PROPOSED NEW FACTORY SITE AT PRESCANE LTD, CHIKWAWA

MALAWI

PREPARED BY: ISHMAEL NG’OMA Email: ishmaelngoma@poly.ac.mw

Cell: 0888528690

August 2015

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1.0 INTRODUCTION

1.1 General

PRESSCANE LIMITED contacted The Malawi Polytechnic, Civil Engineering

Department to conduct geotechnical investigation surveys on soils at the

Proposed New Factory Site close to the weighbridge at Presscane Ethanol

Distillery Complex in Chikwawa District of Malawi.

Site reconnaissance, in situ (on site) testing and soil sampling were carried out

on 09th August 2015. Laboratory testing proceeded immediately at the

Malawi Polytechnic, Civil Engineering Laboratory in Blantyre.

1.2 Project Description

It is our understanding that the project involves the construction of new

factory buildings at Presscane Ethanol Distillery Complex in Chikwawa District.

It is also our understanding that the structures to be built will be ground level

structures with no storeys and that the structures will be mainly load bearing

walls resting on standard mass concrete strip footings.

1.3 Objectives of the Soil Investigation Survey

The purpose of the geotechnical exploration exercise was:

1. To determine the subsoil conditions under the proposed new site for the

construction of factory buildings.

2. To determine the engineering properties of the soil.

3. To comment on the type of foundation to be adopted.

4. To assess the bearing capacity of the soil in line with standard strip

footings of the width 690mm.

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2.0 SOIL SAMPLING AND TESTING

Three trial pits for soil sampling and measurement of insitu strength of soils by

DCP (Dynamic Cone Penetrometer) were dug around the proposed site. The

trial pits were dug in order to reveal the soil profile and get samples for

laboratory testing. Location for the three trial pits were agreed with Richard

Dikamdima of PressCane. The trial pits were approximately 2.0m deep and

two (2) samples were collected from each trial pit at 1.0m and 2.0m depths.

Samples collected were taken to Polytechnic Laboratory and tested for

Atterberg Limits (Plasticity Index), Particle Size Distribution (Wet Sieve Analysis)

and Linear Shrinkage.

It was NOT possible to collect undisturbed samples for triaxial testing because

the soils were loose to medium dense making it impossible to penetrate the

soil sampling tubes for undisturbed sample extraction. Therefore, due to the

nature of the soils, triaxial tests were NOT done.

3.0 OBSERVATIONS AND DISCUSSIONS

Observations on all the pits namely; Pit #1, Pit #2 & Pit #3 indicated that the

soils were basically loose sand near the surface and medium dense silty sand

soils of non plastic beyond 0.5m which was relatively difficult to excavate.

Basically the surface of the ground to about 0.3m deep was very weak made

up mainly of loose sand. Below 1.0m it was difficult to do the DCP penetration

tests because the soils were made of medium dense silty sand.

For Trial Pit #1 and Trial Pit #2, DCP test results indicated a Penetration Index

of less than 8mm/blow (approximate CBR of 22%) and computing to

approximate Safe Bearing Pressure of 210kPa which means the ground is

strong and very stable.

For Trial Pit #3, DCP test results indicated a Penetration Index of 13mm/blow

(approximate CBR of 13%) and computing to approximate Safe Bearing

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Pressure of 165kPa which means the ground is relatively weaker compared to

the other pits i.e. Pit#1 & Pit #2 (Sketch Map attached to the summary of

results sheet).

The Natural Moisture Content (insitu) ranges from 2.5% - 5.9% with the

Atterberg Limits (Plasticity Index) showing that the soils are Non Plastic (NP).

Where necessary, materials excavated from all the three trial pits can be

used as fill provided that they are compacted to their Maximum Dry Density

(MDD) at their Optimum Moisture Content (OMC).

4.0 TRIAL PITS

Loose sand soils were observed to a depth of about 0.3m from all the three

trial pits as shown below;

Trial Pit #1; Loose Sand Soils to less than 0.3m deep

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Trial Pit #2; Loose Sand Soils to less than 0.3m deep

Trial Pit #1; Medium Dense Silty Sand Soils of Non Plastic beyond 1.0m deep

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Trial Pit #3; Medium Dense Silty Sand Soils of Non Plastic beyond 1.0m deep

Trial Pit #1; Difficult to excavate layer after 1.0m deep

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Trial Pit #2 with Soil Profile similar to Trial Pit #1 as shown above

Trial Pit #3 with Soil Profile similar to Trial Pit #s1 & 2 as shown above

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Trial Pit #3; DCP Penetration Test in progress

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5.0 RECOMMENDATIONS

It can be noted that the proposed site is dominated loose to medium dense

silty soils which overlay the hard to cultivate material beyond 1.0m deep.

Where necessary, materials excavated from all the three trial pits can be

used as fill provided that they are compacted to their Maximum Dry Density

(MDD) at their Optimum Moisture Content (OMC).

The recommendation is based on the field and laboratory test results. From

field observations and findings, the soils at the proposed site are adequate to

support normal strip footing foundation.

The design of any foundation base, considers the permissible Bearing Pressure

on the ground that corresponds to a service stress and its maximum value

that can be supported without excessive deformation taking place.

Therefore, the type and shape of the loading determines the shape of the

foundation.

The maximum expected load from the factory buildings is NOT known.

However the foundation can be erected at the ranges of between 1.5m -

2.0m deep. The approximate Bearing Pressure of the soil on a proposed

factory site ranges between 165kPa - 210kPa.

6.0 REFERENCES

Barnes G, E (2000). Soil Mechanics: Principles and Practice. 2nd Ed.

MacmillianPressLtd, London

BS 1377, 1990 Methods of Testing for Soils for Civil Engineering Purposes

Clayton C.R.I. (1999). The standard Penetration test (SPT); Method and Use.

CIRIAreport no. Report/CP/7 Great Britain

Craig R.F (2004). Soil Mechanics.7th Ed. Spon Press. London

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7.0 APPENDICES (Attachments through email & hard copies)

1. Particle Size Distribution test results - 3 pits (6 copies)

2. DCP test results - 3 pits (3 copies)

3. Linear Shrinkage test results (1 copy)

4. Moisture Content test result (1 copy)

5. Sketch Map (1 copy)

6. Table showing summary of the results & the Sketch Map (1 copy)

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